Im putting outlets into my new Shop, planning for a 1" EMT conduit containing three circuits running from the panel box: A 20A 120V, B 30A 240V and C 50A 120/240, so 7 conductors plus the conduit ground.

The outlets will be attached to the conduit and mounted similar to the installation in this photo.


One difference is my shop has the continuous hoop connections up at the 3 foot level allowing more bolt holes (like the lowest part of this picture). The Conduit will be hung on P Clamps every 2' attached to the existing metal bolts holding the building "hoops" together.

I Plan on putting 4"x4" boxes every 4' with either a 120V dual outlet or an appropriate 240V single outlet (either NEMA 6-30 or 14-50 for the two circuit types). Since each circuit carries different size conductors it should be easy to keep them straight (12AWG, 10AWG and 6 AWG). Two different sets of circuits will run one clockwise and one counterclockwise out from the panel for 6 circuits total. Additional individual special circuits will be run for lighting (120V), a 240V compressor, and a 240V cooler. Total of ~15 spaces in my 30 space panel.

I'm in Tucson AZ under the 2017 NEC for this. Is there anything I'm doing here which seems concerning to the experts online or any additional advice I should consider?

After-report: Some more detail on How I ended up running along the Quonset hut interior. (The small handy box is just for splicing to make the pull easier) And yes there is a ground wire even though its not supposed to be required using EMT; however My inspector wanted it in [see this question: https://diy.stackexchange.com/questions/207090/conduit-for-ground-in-metal-shop ]

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  • 3
    Have you done a box fill calculation for your circuit? I think you'll have too many conductors and devices for a normal-depth 4x4 box at some points on your planned circuit. Try inputting your boxes into an online box fill calculator and see if they are within 28cm3 or if you need to make adjustments. Sep 21, 2020 at 22:04
  • 1
    good call! I had not done that, just ran it and I will need to go the deep 4x4 boxes to work. (I calc 30 cu-inches so 4x4x1.125)
    – mark f
    Sep 21, 2020 at 22:11
  • The final box will be the big "RV" NEMA14-50 plug, so by that point the run is over (it will need a bigger box by itself). I better look more carefully at each planned box and its yolk and wire loading.
    – mark f
    Sep 21, 2020 at 22:22
  • I was planning only the metal conduit as the ground path. Also, the entire building is also tied to the conduit, receptacle ground and the panel box ground...
    – mark f
    Sep 21, 2020 at 22:33
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    The conduit will be fine as the grounding path! Be prepared to show the inspector your derating because you have more than 3 current carrying conductors in your pipe, you did not mention wire type but for your derate you can use the 90 degree table if you use thhn or other wire type rated for 90 degrees. Since 12 awg and 10awg is limited by code they are usually fine up to 8 conductors for the 6awg I would check just to make sure. Did you check your total conductor fill? Annex’s only the back of the book have individual values you will need to make sure you don’t go over there also
    – Ed Beal
    Sep 22, 2020 at 1:26

1 Answer 1


I ended up riveting the boxes to brackets and bolting those to the existing "grain bin" bolts holding the Quonset Hut Hoops together. Then ran EMT through them anchored to other bolts via P-Clamps. An important note: The boxes need to be secured rigidly, not merely hung on the conduit and supported by conduit (this would not be allowed)

I posted a picture of the final configuration in the question.

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